Allow matches to merge with default values.
I like a lot the merge matches features for hash and array parameters. It would be even better though is we could merge the overrides with the default values as well.
For example: I have user accounts, ssh keys set through hashes and I have a default set of user and keys for all servers and then override specific groups and hosts but currently I have to include same default users in every override. I would like to have a check box to override with default and just add new values in overrides.
Refs #10731 - adding match_default to smart variables and smart class parameters